82 ANNUAL OF SCIENTIFIC DISCOVERY. 



plate, the cracks radiating, starlike, from the centre. The last shot 

 broke the plate eighteen inches from the bottom. 



The next plate tested was a 3-inch, four feet in length by three 

 broad, and weighing 13 cwt. 1 qr., a 40-pounder being used at one 

 hundred yards range. The first shot discharged indented the plate 

 about 2-| inches and slightly fractured it on its reverse. The fourth 

 plate fired at was a 21-inch, of the same length and breadth as the 

 last, weighing 10 cwt. 3 qrs., at the same range, but commencing 

 with a 25-pounder. The first shot indented the plate If inches, but 

 made no fracture. The second made an indentation of 21 inches, and 

 fractured the plate on its reverse. The third struck the lower part 

 of the plate but did no damage. The 40-pounder was now pointed 

 at the plate, and its shot tore a passage through. The last plate 

 tested was a 2-inch, of the same length and breadth as the two pre- 

 ceding ones, weighing 8 cwt. 2 qrs. 22 Ibs. The range was the same, 

 commencing with a 1 2-pounder. The first shot indented the plate an 

 inch and a half; the second fractured the plate, part of the shot re- 

 maining in it ; and the third slightly fractured it. The fourth and 

 last shot was made from the 40-pounder, and passed through the 

 plate. 



On another occasion the Committee, in order to ascertain the best 

 quality of material, best thickness of metal, and the best mode of 

 manufacturing iron plates, invited the leading manufacturers of the 

 country to place before them specimens of iron plates which they 

 considered best adapted for the purposes required. Plates, varying 

 in thickness from one-quarter inch to ten inches, were sent in. Sir 

 John Hay, in a report on these experiments, made to the British 

 Association (1861), stated, that the committee found "that the 

 steely description of metal, that was to say, metal which had been 

 hardened, and went by the names of semi-steel, homogeneous iron, 

 etc., up to a thickness of three-quarters of an inch, possessed great 

 resisting powers, but after that thickness this description of metal 

 was not so well qualified to resist a blow of a projectile as wrought 

 iron of the best kind. This having been ascertained, another law 

 had been pointed out to them, which they were not yet in a position 

 fully to recognize. It was, that the resistance of the plating in- 

 creased with the square of its thickness. Thus, if the resistance of 

 a plate one inch in thickness was equal to one, the resistance of a 

 plate two inches in thickness would be four ; four inches in thick- 

 ness, sixteen ; and six inches in thickness, thirty-six. Considerable 

 difficulty was felt in fastening the plates upon the sides of the ves- 

 sels, as it was felt that all holes drilled in them were a source of 

 weakness. Their great fear was not of a solid missile being driven 

 through the ships' sides, but of the possible material the shot might 

 contain. They could scarcely hope effectually to exclude cold shot, 

 but they did think it was possible so to construct a ship and so to 

 plate it, that a hollow missile impinging upon its sides would be 

 broken to pieces, and consequently they hoped to be able to exclude 

 all shells, red-hot shot, and shot filled with liquid iron, which were 

 amongst the most terrible weapons of modern warfare. 



The Committee had also observed that at whatever angle the tar- 

 gets were placed, the fracture made by the Armstrong gun was just 



